An important agricultural issue is management of crop-destroying insects. Use of chemical pesticides is the primary solution for controlling insects and, in 1999, more than 200 million tons of such pesticides were applied in the US. Unfortunately, use of chemical pesticides is a potential cause of health and environmental problems, especially if the pesticides get into the soil and water supply.
Concern over the potential hazards of chemical pesticides has generated interest in alternative approaches for insect pest control. Entomopathogenic nematodes, in the families Steinernematidae and Heterorhabditidae, are lethal insect parasites that have emerged as excellent potential biological control agents for a number of reasons. Entomopathogenic nematodes cause rapid mortality of a broad range of insects. The nematodes are easily mass produced. Entomopathogenic nematodes are also safe for mammals. In fact the US Environmental Protection Agency (EPA) has exempted entomopathogenic steinernematids and heterorhabditids from registration and regulation requirements, thus simplifying considerably the application, development and commercialization of new nematode formulations.
Entomopathogenic nematodes have a symbiotic association (i.e., living together with mutual advantage to both organisms) with bacteria in the family Enterobacteriaceae. The free living stage of the nematodes, called the infective juvenile (IJ) or dauer, seeks out and infects a host insect. Following penetration into the insect, the IJs release the bacteria into the insect blood stream. The bacteria multiply rapidly, killing the insect host within 24-48 hours. Nematodes complete 2-3 generations in the cadaver and new IJs are produced that then leave the insect and seek out new hosts.
Nematodes have been used as insecticides in high value crops, including citrus, cranberries, mushrooms, greenhouse ornamentals, and turfgrasses. The application of these nematodes to soil or plants provides levels of insect control comparable to that of chemical insecticides. The natural habitat of entomopathogenic nematodes is the soil. Nematodes can survive in various conditions of moisture, temperature, texture and chemical composition associated with different soil types. Consequently, nematodes are found on all continents, except Antarctica, and at nearly all latitudes and altitudes. Considered as a group, entomopathogenic nematodes are currently the second most utilized biocontrol agent against insect pests, after Bacillus thuringiensis. 
Although nematodes are excellent biocontrol agents, their present use has significant limitations. Because the natural habitat of entomopathogenic nematodes is the soil, nematodes are not well adapted to tolerate direct sunlight, ultraviolet (UV) irradiation, or low humidity (i.e.,<80% relative humidity) and can withstand only limited exposure to these conditions. The sensitivity of nematodes to inactivation by extremes of the physical environment prevents them from reaching their full potential as insecticides, in particular when applied to exposed surfaces, such as foliage. Therefore, successful use of nematodes for insect control is currently limited principally to soil or protected environments, where the nematodes are shielded from sunlight and rapid drying.
In summary, although nematode activity on plant foliage is possible, outdoor activity of the infective juvenile nematodes (IJs) on the leaf is limited to several hours because of their inability to withstand the physical environment. This is a situation that is economically unacceptable. Although numerous formulations have been developed to improve the nematode activity on the crop and in storage, major improvements are still very much needed.